On internal combustion engines configured to recirculate exhaust gas, whose recirculation amount depends on an operating condition, back to the intake system, such internal combustion engines, which are configured to diagnose a failure in an EGR control valve disposed in an EGR passage for recirculating exhaust gas from the exhaust system to the intake system, are well known.
For instance, Patent document 1 discloses a technology in which a failure diagnosis for an EGR control valve, which is disposed in an EGR passage configured to connect an exhaust passage and an intake passage, is performed. As a result of the failure diagnosis, when it is determined that an open failure, in which the EGR control valve has been fixed in its open state, is occurring, fail-safe control is executed for limiting an output of the internal combustion engine.
In this Patent document 1, by virtue of execution of the above-mentioned fail-safe control, it is possible to avoid high output operation of the internal combustion engine when the EGR control valve has been fixed in the open state. Hence, there is a less tendency for the EGR control valve and the intake system to be excessively heated owing to high temperature EGR gas, and thus it is possible to prevent a secondary failure in the EGR control valve and a deterioration in performance of the internal combustion engine.
However, in the Patent document 1 there is a problem that it is impossible to prevent an engine stall, which may occur owing to a deterioration in combustion and/or a misfire caused by an excessive EGR (exhaust-gas-recirculation) rate resulting from the EGR control valve fixed or stuck in the open state.